The present invention relates to host position control among a plurality of local area networks (referred to as LANs, hereinafter) in a system in which the LANs are interconnected by a bridge, and more particularly to a method and a system for controlling a mobile host which uses a radio medium.
In a bridge device for interconnecting LANs, a mobile host connected to these LANs is confirmed by monitoring a transmission originating address SA (Source Address) for a frame flowing on each of the LANs. The bridge device provides efficient frame transfer based on information regarding the position of the mobile host, which is obtained in the above-described manner.
Referring to FIG. 7 which illustrates the constitution of a bridge device 13, the bridge device 13 shown includes a learning function table 14, an exchanging/learning control section 15 and line connecting sections 16 and 17. The line connecting sections 16 and 17 perform connection with each LAN. The learning function table 14 registers the address of each mobile host connected to LANs (1) 11 and (2) 12. The exchanging/learning control section 15 absorbs a difference in protocol between the LANs and controls address registration performed by the learning function table 14.
When each LAN as a network is constituted by using a multiple address medium, for instance Ethernet presented by Xerox Company of US, frame transfer is performed under the following rules.
1. If the destination address DA (Destination Address) of a received frame is a multiple address, multiple address transfer is performed for all LANs other than a LAN which has received the frame.
2. Regarding a mobile host specified by the destination address DA of a received frame, if a LAN to which the mobile host is connected is determined and this LAN is discovered to be different from a LAN which has received the frame, transfer is performed for the LAN to which the specified mobile host is connected.
3. Regarding a mobile host specified by the destination address DA of a received frame, if a LAN to which the mobile host is connected is determined and this LAN is identical to the LAN which has received the frame, since all the nodes of this LAN can receive the frame, this received frame which needs not to be transferred is canceled.
4. Regarding a mobile host specified by the destination address DA of a received frame, if a LAN to which the mobile host is connected is not determined, transfer is performed for all LANs other the LAN which has received the frame.
If a mobile host is moved among LANs, the bridge device determines that the mobile host is connected to a plurality of LANs. Consequently, a contradiction occurs in positional information. Efforts have been made to solve this problem. For example, referring to JP-A-217141/1992 or JP-A-154335/1992, there is disclosed a bridge device, which monitors a frame flowing through segments and renews information regarding the position of a mobile host immediately after detection of the movement of the mobile host.
However, in the case of the LAN using a radio medium, a destination which the mobile host has reached may be outside the range of radio transmission or the mobile host itself may not send any frames. In such a case, in the prior art, positional information is not renewed and useless radio traffic is produced because of the continuance of frame transfer by the bridge device. Consequently, radio wave resources are wasted for nothing.
Such a situation occurs because if the mobile host is not under the control of the bridge device, unnecessary frame transfer is not recognized. Therefore, wasteful consumption of power by the bridge device has been another problem to be solved.